Mechanical Separates and Their Fractions in the Soil Profile: I. Variability in Chemical Composition and Its Pedogenic and Agropedologic Implications

I. VARIABILITY IN CHEMICAL COMPOSITION AND ITS PEDOGENIC AND AGROPEDOLOGIC IMPLICATIONS J. S. JOFFE AND R. KuNIN MOST investigations on mechanical separates of the soil have dealt with the physical aspects of the subject, with no relation to pedogenesis and agropedologic implications. In recent years valuable information has been made available on the physical and some chemical attributes of the mechanical separates in the soil profile. It has been increasingly clearly recognized that it was not enough to know the quantitative relationships of the mechanical separates and just a few isolated properties, important as they might be, such as N, P, K, Ca, and Mg content (most analyses are limited to NPK) and ion exchange properties. Other information, such as the physical properties of the separates in their relation to hydrologic and aeration conditions, is being sought. Moreover, the mineralogic and more detailed analyses on the chemical composition of the separates and some fractions of these are the order of the day. All such information, collected on a profile basis, is now being used in a practical way in tracing many of the • perplexing problems of the farmer (8). From a thorough review of the literature it is apparent that data relating to pedogenesis and soil fertlity aspects are scarce. Reference will be made in this paper only to studies having some bearing on the subject under discussion. In these studies comprehensive bibliographies to the subject of the mechanical separates of the soil are given. This paper deals with the variability in chemical composition of the soil separates and some of their fractions.